The long term goals of this project are to isolate, characterize and study the expression of the human actin genes in both normal and pathological muscle and in cell differentiation. Utilizing the information obtained from these studies, we intend to design experiments which will help provide an understanding of how mammals in general, and humans in particular, use the actin multigene family to produce the various cellular structures which result from actin gene expression. We plan to isolate all the actin genes in the human genome. In addition to the cardiac-, skeletal- and cytoskeletal beta-actin gene already isolated, we will identify the cytoskeletal gamma- and two smooth muscle-actin genes. We will determine if the human genome encodes more than six different actin isotypes. The functional actin genes will be characterized in terms of the organization of coding and non-coding regions, the nucleotide sequence of putative RNA polymerase promoter sites at the 5' end of the genes and their chromosomal location. The regulation of actin gene expression will be evaluated to determine (1) how many actin genes are utilized to produce the cytoskeletal actins, (2) how many actin genes are regulated during human myogenesis in cell culture and (3) if transcription of the actin gene family is modulated in response to neoplastic transformation. We will define the regions of the human cardiac- and skeletal-actin genes which are responsible for their regulation during myogenesis. The human cardiac actin gene will be introduced into non-muscle cells and the ability of these cells to discriminate between a sarcomeric actin and endogenous non-muscle actin will be evaluated. We will explore the possibility of repressing the synthesis of specific actins by inducing expression of isotype specific anti-sense sequences.